ESLint Plugin De Morgan

An ESLint plugin that enforces logical consistency by transforming negated boolean expressions according to De Morgan’s laws.

This plugin automatically rewrites negated conjunctions and disjunctions to improve code clarity and reduce potential logical errors.

In Boolean algebra, De Morgan’s laws are two transformation rules that are both valid rules of inference. They are named after Augustus De Morgan and are fundamental in the fields of mathematics, computer science, and digital logic. The laws state that:

First Law:

$\neg (A \land B) \equiv (\neg A) \lor (\neg B)$

Second Law:

$\neg (A \lor B) \equiv (\neg A) \land (\neg B)$

Using these principles, the plugin provides two ESLint rules:

• no-negated-conjunction — Transforms negated conjunctions (i.e. expressions of the form !(A && B)) into the equivalent disjunction of negations (!A || !B).
• no-negated-disjunction — Transforms negated disjunctions (i.e. expressions of the form !(A || B)) into the equivalent conjunction of negations (!A && !B).

These transformations are grounded in Boolean algebra and can help make the logic of your code more explicit and easier to understand.

De Morgan’s laws are a cornerstone of Boolean algebra and have several practical benefits in programming:

• Clarity: Rewriting complex negations often results in expressions that more clearly communicate the underlying logic.

For example:

if (!(a && !b && c >= 10 && d !== e)) {
  /* ... */
}

Becomes:

if (!a || b || c < 10 || d === e) {
  /* ... */
}

• Avoiding Logical Errors: When dealing with nested logical expressions, small mistakes in the placement of negations can lead to subtle bugs. By enforcing a consistent style based on well-known laws, the plugin helps reduce such errors.

• Simplification: In some cases, the transformed expression may be simpler to evaluate and optimize, both for human readers and for compilers / interpreters.

You'll first need to install ESLint:

npm install --save-dev eslint

Next, install eslint-plugin-de-morgan:

npm install --save-dev eslint-plugin-de-morgan

The easiest way to use eslint-plugin-de-morgan is to use ready-made config.

import deMorgan from 'eslint-plugin-de-morgan'

export default [
  deMorgan.configs.recommended,
]

module.exports = {
  extends: [
    'plugin:de-morgan/recommended-legacy',
  ],
}

🔧 Automatically fixable by the --fix CLI option.

• De Morgan’s Laws
• Boolean Algebra

This plugin is following Semantic Versioning and ESLint's Semantic Versioning Policy.

See Contributing Guide.

MIT © Azat S.